Alberti, Leone Battista, Architecture, 1755

Page concordance

< >
Scan Original
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
< >
page |< < of 320 > >|
    <archimedes>
      <text>
        <body>
          <chap>
            <p type="main">
              <s>
                <pb xlink:href="003/01/073.jpg" pagenum="57"/>
              ſet with their Heads one againſt the other, and
                <lb/>
              their Feet ſet wide, would, if faſtened at Top,
                <lb/>
              ſtand, very firm, by means of the Equalneſs
                <lb/>
              of their Weight: They were pleaſed with this
                <lb/>
              Invention, and began to make their Roofs
                <lb/>
              in the ſame Manner, to throw off the Rain,
                <lb/>
              both Ways. </s>
              <s>Afterwards, perhaps, not being
                <lb/>
              able to cover a wider Space for want of Beams
                <lb/>
              long enough, they put between the Heads of
                <lb/>
              theſe two Beams another croſſways at Top,
                <lb/>
              ſo that they made a Figure much like that of
                <lb/>
              the Greek Letter
                <foreign lang="grc">π,</foreign>
              and this middle Beam
                <lb/>
              they might call a Wedge; and as this ſuc­
                <lb/>
              ceeded very well, they multiplyed the Wedges,
                <lb/>
              and thus made a Kind of Arch, whoſe Figure
                <lb/>
              mightily delighted them. </s>
              <s>Then transferring
                <lb/>
              the ſame Method to their Works of Stone, con­
                <lb/>
              tinuing to multiply the Wedges, they made
                <lb/>
              an entire Arch, which muſt be allowed to be
                <lb/>
              nothing elſe but a Conjunction of a Number
                <lb/>
              of Wedges, whereof ſome ſtanding with their
                <lb/>
              Heads below the Arch, are called the Foot of
                <lb/>
              the Arch, thoſe in the Middle above, the Key
                <lb/>
              of the Arch, and thoſe on the Sides, the Turn,
                <lb/>
              or Ribs of the Arch. </s>
              <s>It will not be improper
                <lb/>
              here to repeat what we ſaid in the firſt Book
                <lb/>
              upon this Subject: There are different Sorts
                <lb/>
              of Arches, the Entire, is the full half of a
                <lb/>
              Circle, or that whoſe Chord runs through the
                <lb/>
              Centre of the Circle; there is another which
                <lb/>
              approaches more to the Nature of a Beam than
                <lb/>
              of an Arch, which we call the Imperfect, or
                <lb/>
              diminiſhed Arch, becauſe it is not a compleat
                <lb/>
              Semi-circle; but a determinate Part leſs,
                <lb/>
              having its Chord above the Centre, and at
                <lb/>
              ſome Diſtance from it. </s>
              <s>There is alſo the
                <lb/>
              Compoſite Arch, called by ſome the Angular,
                <lb/>
              and by others an Arch compſed of two Arches
                <lb/>
              leſs than Semi-circles; and its Chord has the
                <lb/>
              two Centres of two Curve Lines, which
                <lb/>
              mutually interſect each other. </s>
              <s>That the Entire
                <lb/>
              Arch is the Strongeſt of all, appears not only
                <lb/>
              from Experience, but Reaſon; for I do not
                <lb/>
              ſee how it can poſſibly diſunite of itſelf, unleſs
                <lb/>
              one Wedge ſhoves out another, which they are
                <lb/>
              ſo far from doing, that they aſſiſt and ſupport
                <lb/>
              one another. </s>
              <s>And indeed, if they were to go
                <lb/>
              about any ſuch Violence, they would be pre­
                <lb/>
              vented by the very Nature of Ponderoſity, by
                <lb/>
              which they are preſſed downwards, either by
                <lb/>
              ſome Superſtructure, or by that which is in the
                <lb/>
              Wedges themſelves. </s>
              <s>This makes
                <emph type="italics"/>
              Varro
                <emph.end type="italics"/>
              ſay,
                <lb/>
              that in Arches, the Work on the right Hand
                <lb/>
              is keptup no leſs by that on the Left, than the
                <lb/>
              Work on the Left is by that on the Right. </s>
              <s>And
                <lb/>
              if we look only into the Thing itſelf; how is
                <lb/>
              it poſſible for the middle Wedge at Top, which
                <lb/>
              is the Key-ſtone to the Whole, to thruſt out
                <lb/>
              either of the two next Side Wedges, or how
                <lb/>
              can that be driven out of its Place by them?
                <lb/>
              </s>
              <s>The next Wedges alſo in the Turn of the
                <lb/>
              Arch, being juſtly counterpoiſed, will ſurely
                <lb/>
              ſtand to their Duty; and laſtly, how can the
                <lb/>
              two Wedges under the two Feet of the Arch,
                <lb/>
              ever be moved while the upper ones ſtand firm?
                <lb/>
              </s>
              <s>Therefore we have no need of a Cord, or Bar
                <lb/>
              in an entire Arch, becauſe it ſupports itſelf
                <lb/>
              by its own Strength; but in diminiſh'd
                <lb/>
              Arches there is Occaſion either for an Iron
                <lb/>
              Chain or Bar, or for an Extenſion of Wall on
                <lb/>
              both Sides, that may have the Effect of a Bar
                <lb/>
              to ſupply the Want of Strength, that there is
                <lb/>
              in the diminiſh'd Arch, and make it equal to
                <lb/>
              the Entire. </s>
              <s>The ancient Architects always
                <lb/>
              uſe theſe Precautions, and where-ever it was
                <lb/>
              poſſible, conſtantly ſecured their diminiſh'd
                <lb/>
              Arches, by ſetting them in a good Body of
                <lb/>
              Wall. </s>
              <s>They alſo endeavour'd, if they had an
                <lb/>
              Opportunity, to turn their imperfect Arches
                <lb/>
              upon a ſtrait Beam; and over theſe imperfect
                <lb/>
              ones, they uſed to turn entire Arches, which
                <lb/>
              protected the diminiſhed ones which were
                <lb/>
              within them, and took upon themſelves the
                <lb/>
              Burthen of the Superſtructure. </s>
              <s>As for Com­
                <lb/>
              poſite Arches, we do not find any of them in
                <lb/>
              the Buildings of the Ancients; ſome think
                <lb/>
              them not amiſs for the Apertures in Towers;
                <lb/>
              becauſe they ſuppoſe they will cleave
                <lb/>
              the great Weight that is laid upon
                <lb/>
              them, as the Prow of a Ship does the Water,
                <lb/>
              and that they are rather ſtrengthened than op­
                <lb/>
              preſs'd by it.</s>
            </p>
            <p type="main">
              <s>THE Stones uſed in Building an Arch,
                <lb/>
              ſhould be every Way the biggeſt that can be
                <lb/>
              got; becauſe the Parts of any Body that are
                <lb/>
              united and compacted by Nature, are more
                <lb/>
              inſeparable than thoſe which are join'd and
                <lb/>
              cemented by Art. </s>
              <s>The Stones alſo ought to
                <lb/>
              be equal on both Sides, as if they were balan­
                <lb/>
              ced with reſpect to their Fronts, Sizes, Weight,
                <lb/>
              and the like. </s>
              <s>If you are to make a Portico, and
                <lb/>
              to draw ſeveral Arches over continued Aper­
                <lb/>
              tures, from the Capitals of Columns, never let
                <lb/>
              the Seat from which two or more Arches are
                <lb/>
              to riſe, be made of two Pieces, or of as many
                <lb/>
              as there are to be Arches, but only of one
                <lb/>
              ſingle Stone, and that as ſtrong as may be, to
                <lb/>
              hold together the Feet of all the Arches. </s>
              <s>The
                <lb/>
              ſecond Stones in the Arch, which riſe next to
                <lb/>
              theſe, if they are large Pieces, muſt be ſet </s>
            </p>
          </chap>
        </body>
      </text>
    </archimedes>
Impressum